Allow remote-to-remote sync pairs

web/src/pages/SyncPairs.tsx

@@ -111,6 +111,14 @@ export default function SyncPairs() {
       toast.error('Source and destination paths are required');
       return;
     }
+    if (
+      form.source_machine_id !== null &&
+      form.dest_machine_id !== null &&
+      form.source_machine_id === form.dest_machine_id
+    ) {
+      toast.error('Source and destination cannot be the same machine');
+      return;
+    }
     setLoading(true);
     try {
       await api(form.id ? `/api/sync-pairs/${form.id}` : '/api/sync-pairs', {
@@ -325,6 +333,9 @@ export default function SyncPairs() {
                       ))}
                     </SelectContent>
                   </Select>
+                  <p className="text-xs text-fg-subtle">
+                    Where the data lives. Pick <span className="font-medium">Local server</span> if it&apos;s on this machine, otherwise the remote machine holding the data.
+                  </p>
                 </div>
                 <div className="space-y-1.5">
                   <Label htmlFor="sp-dest-machine">Dest Machine</Label>
@@ -346,6 +357,9 @@ export default function SyncPairs() {
                       ))}
                     </SelectContent>
                   </Select>
+                  <p className="text-xs text-fg-subtle">
+                    Where to copy the data. Can be the same machine (no-op) or any remote. Remote-to-remote is supported.
+                  </p>
                 </div>
               </div>
               <div className="grid grid-cols-2 gap-3">